#define _CRT_SECURE_NO_WARNINGS 1
#include<bits/stdc++.h>
using namespace std;

int main() {
    int data[200];
    for (int i = 0; i < 200; i++) data[i] = 4 * i + 6;
    int x; cin >> x;
    int l = -1, r = 199;
    while (l + 1 != r) {
        int mid = (l + r) >> 1;
        if (data[mid] >= x) r = mid;
        else l = mid;
    }
    cout << r << '\n';
    return 0;
}